lshell(1)

NAME
lshell - Limited Shell

SYNOPSIS
lshell [OPTIONS]

DESCRIPTION
lshell provides a limited shell configured per user. The configuration is done quite simply using a configuration file. You can also use lshell within scripts by adding the appropriate shebang (#!/usr/bin/lshell) to your script file. Coupled with ssh's authorized_keys or with /etc/shells and /etc/passwd , it becomes very easy to restrict user's access to a limited set of command.

OPTIONS

--config <FILE>
    Specify config file

--log <DIR>
    Specify the log directory

--<param> <value>
    where <param> is *any* config file parameter

-h, --help
    Show help message

--version
    Show version

CONFIGURATION
You can configure lshell through its configuration file:

    On Linux -> /etc/lshell.conf
    On *BSD  -> /usr/{pkg,local}/etc/lshell.conf

The configuration is dynamically reloaded. Which means that you can edit the configuration, and all the connected users will automatically load it. In case you are using multiple configuration files (see include_dir), you will need to refresh the main configuration's timestamp, in order to reload the configuration:

    touch /path/to/lshell.conf

lshell configuration has 4 types of sections:

    [global]   -> lshell system configuration (only 1)
    [default]  -> lshell default user configuration (only 1)
    [foo]      -> UNIX username "foo" specific configuration
    [grp:bar]  -> UNIX groupname "bar" specific configuration

Order of priority when loading preferences is the following:

    1- User configuration
    2- Group configuration
    3- Default configuration

  [global]

logpath
    config path (default is /var/log/lshell/)

loglevel
    0, 1, 2, 3 or 4 (0: no logs -> 4: logs everything)

logfilename
    - set to syslog in order to log to syslog
    - set log file name, e.g. %u-%y%m%d (i.e foo-20091009.log): %u -> username
    %d -> day [1..31]
    %m -> month [1..12]
    %y -> year [00..99]
    %h -> time [00:00..23:59]

syslogname
    in case you are using syslog, set your logname (default: lshell)

include_dir
    include a directory containing multiple configuration files. These files can only contain default/user/group configuration. The global configuration will only be loaded from the default configuration file. This variable will be expanded (e.g. /path/*.conf).

path_noexec
    set path to sudo noexec library. This path is usually autodetected, only set this variable to use alternate path. If set and the shared object is not found, lshell will exit immediately. Otherwise, please check your logs to verify that a standard path is detected. while this should not be a common practice, setting this variable to an empty string will disable LD_PRELOAD prepend of the commands. This is done at your own risk, as lshell becomes easily breached using some commands like find(1) using the -exec flag.

  [default] and/or [username] and/or [grp:groupname]

aliases
    command aliases list (similar to bash's alias directive)

allowed
    A list of allowed commands, or set to 'all' to allow all commands in the user's PATH.
    - If a command is specified without arguments (e.g., 'echo'), the command is allowed to run with any arguments.
    - If a command is specified with exact arguments (e.g., 'echo asd'), only that specific command with those arguments will be allowed.
    - To allow all commands in the user's PATH, use the value 'all'.
if sudo(8) is installed and sudo_noexec.so is available, it will be loaded before running every command, preventing it from running further commands itself. If not available, beware of commands like vim/find/more/etc. that will allow users to execute code (e.g. /bin/sh) from within the application, thus easily escaping lshell. See variable 'path_noexec' to use an alternative path to library.

allowed_shell_escape
    a list of the allowed commands that are permitted to execute other programs (e.g. shell scripts with exec(3)). Setting this variable to 'all' is NOT allowed. Warning: do not put here any command that can execute arbitrary commands (e.g. find, vim, xargs). important: commands defined in 'allowed_shell_escape' override their definition in the 'allowed' variable.

allowed_file_extension
    a list of allowed file extensions that can be provided in the command line. If a list of allowed extensions is provided, all other file extensions will be disallowed.

allowed_cmd_path
    a list of path; all executable files inside these path will be allowed

disable_exit
    disable user exit, this could be useful when lshell is spawned from another none-restricted shell (e.g. bash)

env_path
    update the environment variable $PATH of the user (optional)

env_vars
    set environment variables (optional)

env_vars_files
    specify a list of files containing environment variables (optional)

forbidden
    a list of forbidden characters or commands

history_file
    set the history filename. A wildcard can be used:
    %u -> username (e.g. '/home/%u/.lhistory')

history_size
    set the maximum size (in lines) of the history file

home_path (deprecated)
    set the home folder of your user. If not specified, the home directory is set to the $HOME environment variable. This variable will be removed in the next version of lshell, please use your system's tools to set a user's home directory. A wildcard can be used:
    %u -> username (e.g. '/home/%u')

intro
    set the introduction to print at login

login_script
    define the script to run at user login

passwd
    password of specific user (default is empty)

path
    list of path to restrict the user geographically. It is possible to use wildcards (e.g. '/var/log/ap*').

prompt
    set the user's prompt format (default: username)
    %u -> username
    %h -> hostname

prompt_short
    set prompt style for current directory - 0, 1 or 2. Default is 0.
    0 -> will show the current directory as compared to home directory ~/current/dir
    1 -> will only show the current directory name
    2 -> will show the complete path to the current directory

LPS1
    LShell supports prompt customization using the $LPS1 environment variable, similar to $PS1 in bash. If $LPS1 is defined, it takes precedence over prompt and allows for dynamic prompt customization using placeholders. Available placeholders need to be prepended with a backslash (\) and include:
    u -> username of the current user
    h -> short hostname (up to first dot)
    H -> full hostname
    w -> current working directory, with home directory replaced by ~
    W -> basename of the current directory
    $ -> prompt symbol (# for root, $ otherwise)
    t -> current time in HH:MM:SS (24-hour format)
    T -> current time in HH:MM:SS (12-hour format)
    A -> current time in HH:MM (24-hour format, without seconds)
    @ -> current time in HH:MM AM/PM format
    d -> current date in Weekday Month Day format (e.g., Mon Mar 01)

overssh list of command allowed to execute over ssh (e.g. rsync, rdiff-backup, scp, etc.)

scp allow or forbid the use of scp connection - set to 1 or 0

scpforce
    force files sent through scp to a specific directory

scp_download
    set to 0 to forbid scp downloads (default is 1)

scp_upload
    set to 0 to forbid scp uploads (default is 1)

sftp
    allow or forbid the use of sftp connection - set to 1 or 0. WARNING: This option will not work if you are using OpenSSH's internal-sftp service (e.g. when configured in chroot)

sudo_commands
    a list of the allowed commands that can be used with sudo(8). If set to 'all', all the 'allowed' commands will be accessible through sudo(8). It is possible to use the -u sudo flag in order to run a command as a different user than the default root.

timer
    a value in seconds for the session timer

strict
    logging strictness. If set to 1, any unknown command is considered as forbidden, and user's warning counter is decreased. If set to 0, command is considered as unknown, and user is only warned (i.e. *** unknown synthax)

warning_counter
    number of warnings when user enters a forbidden value before getting exited from lshell. Set to -1 to disable the counter, and just warn the user.

winscp
    enable support for WinSCP with scp mode (NOT sftp) When enabled, the following parameters will be overridden:
    scp_upload: 1 (uses scp(1) from within session)
    scp_download: 1 (uses scp(1) from within session)
    scpforce: ignored (uses scp(1) from within session)
    forbidden: -[';']
    allowed: +['scp', 'env', 'pwd', 'groups', 'unset', 'unalias']

SHELL BUILTIN COMMANDS
Here is the set of commands that are always available with lshell:

clear
    clears the terminal

export
    name of exported shell variable. Disabled by default, enable it by adding it to allowed commands.

help, ?
    print the list of allowed commands

history
    print the commands history

lpath
    lists all allowed and forbidden path

lsudo
    lists all sudo allowed commands

EXAMPLES

$ lshell
    Tries to run lshell using default ${PREFIX}/etc/lshell.conf as configuration file. If it fails a warning is printed and lshell is interrupted. lshell options are loaded from the configuration file

$ lshell --config /path/to/myconf.file --log /path/to/mylog.log
    This will override the default options specified for configuration and/or log file

$ ./test_script.lsh
    If you include lshell in a script with the shebang (e.g. #!/usr/bin/lshell) and use the `.lsh` extension:

    #!/usr/bin/lshell
    echo "Hello World!"
    Ensure the script has a .lsh extension to indicate it is intended for lshell. This allows for limited shell commands to be executed within the script while maintaining restrictions.

USE CASE
The primary goal of lshell, was to be able to create shell accounts with ssh access and restrict their environment to a couple a needed commands. In this example, User 'foo' and user 'bar' both belong to the 'users' UNIX group:

User foo:
     - must be able to access /usr and /var but not /usr/local
     - user all command in his PATH but 'su'
     - has a warning counter set to 5
     - has his home path set to '/home/users'

User bar:
     - must be able to access /etc and /usr but not /usr/local
     - is allowed default commands plus 'ping' minus 'ls'
     - strictness is set to 1 (meaning he is not allowed to type an unknown command)
In this case, my configuration file will look something like this:

    # CONFIURATION START
    [global]
    logpath         : /var/log/lshell/
    loglevel        : 2
    [default]
    allowed         : ['ls','pwd']
    forbidden       : [';', '&', '|']
    warning_counter : 2
    timer           : 0
    path            : ['/etc', '/usr']
    env_path        : ':/sbin:/usr/bin/'
    scp             : 1 # or 0
    sftp            : 1 # or 0
    overssh         : ['rsync','ls']
    aliases         : {'ls':'ls --color=auto','ll':'ls -l'}
    [grp:users]
    warning_counter : 5
    overssh         : - ['ls']
    [foo]
    allowed         : 'all' - ['su']
    path            : ['/var', '/usr'] - ['/usr/local']
    home_path       : '/home/users'
    [bar]
    allowed         : + ['ping'] - ['ls']
    path            : - ['/usr/local']
    strict          : 1
    scpforce        : '/home/bar/uploads/'
    # CONFIURATION END

NOTES

In order to log a user's warnings into the logging directory (default /var/log/lshell/) , you must firt create the folder (if it doesn't exist yet) and chown it to lshell group:

    # addgroup --system lshell
    # mkdir /var/log/lshell
    # chown :lshell /var/log/lshell
    # chmod 770 /var/log/lshell

then add the user to the lshell group:

    # usermod -aG lshell user_name

In order to set lshell as default shell for a user:

    On Linux:
    # chsh -s /usr/bin/lshell user_name
    On *BSD:
    # chsh -s /usr/{pkg,local}/bin/lshell user_name

AUTHOR
Currently maintained by Ignace Mouzannar (ghantoos)

EMAIL
Feel free to send me your recommendations at <ghantoos@ghantoos.org>